Electric sound reproducer



May 31,1927. 1,630,641

A. A. THOMAS ELECTRIC soUND REPRODUGER Filed Jan. 23, 192e Patented May 31, 1927.

4UNITED `STATES ADQLPH A. THOMAS, or NEW YORK, N. Y. y ELECTRIC SOUND REPRODUCER.

Application led January 23, 1926. Serial No. 83,131.

My invention is for a new and improved sound reproducer, which may be used as a telephone transmitter, as an electric phonograph reproducer, and forv similar purposes.

5 Briefly stated, my invention comprisesa novel form of electromagnetic mechanism 1n Which a vibratory magnetic member produces flux variations. in a magnetic shunt path. This shunt path includes a magnetic core having an airgap, and this core is surrounded by Aa current-generating coil. As the magnetic member vibrates in proximity to the polar faces of the magnet, it varies the magnetic flux through the -coil with amplified eect. This is due to the fact that the magnetic member and the coil are included in two parallel magnetic paths; hence, the vibatory member simultaneously varies the magnetic flux through the two 29 paths in opposite relation. 'That is to say, when the magnetic member moves toward the pole pieces it increases the flux through the main path and simultaneously decreases the ux through the shunt path. The next instant, When the magnetic member recedes from the polar faces, most of the lieldux passes through the coil. Consequently, slight vibrations of the magnetic member produce an amplified magnetic effect on the 3o coil. The current impulses thus generated in the circuit of the coil may be amplified to operate a loudspeaker or used for any other practical purpose.

Tf the instrument of my invention is constructed as a telephone transmitter, the vibratory magnetic member is in the form of an yacoustic diaphragm. In employing my invention for an electric phonograph reproducer, the vibratory member is con- 40 nected to a needle arm.y

lln order to enable those skilled in the artV to understand my invention fully and clearly, I have shown in the accompanying drawings, by way of example, an electric phonograph reproducer constructed in accordance with my invention. In these drawings,

Fig. l shows an inside view of an.. electric phonograph reproducer embodying my invention, a portion ofthis view being taken on section line 1-1 of Fig. 2 for the sake of clearness;

Fig. 2 is a longitudinal cross-section ap- PATENTY OFFICE.

VHEISSUED` proximately lon the broken line 2 2 of Fig. l; Y

Fig. 3 shows a transverse'cross-section on line 3-3 of Fig. l;

Fig. 4 is a detached perspective view showing the construction and arrangement Y of the magnetic pole ieces; and

Fig. 5 shows a slightly modied form of pole pieces to providey a shunt path with an airgap at one endof the coil.

Before proceeding with a detailed description of the drawings, l Want to point .65 out that the various views are on an enlarged scale and the dimensions of the parts have been purposely exaggerated in order to make the yfigures as clear as possible.

The drawings are therefore not to beftake1r70 f as Shop drawings with accurate dimensions.

Such details are relegated to the mechanic.

There is a casing indicated as a Whole by C for carrying the different parts that make up the instrument. This casing may be made of suitable non-magnetic material, such as aluminum or an aluminum alloy, or it may be molded from a composition having the requisite hardness and strength: ln the present instance, the casing is substantially rectangular in shape, and consists of a back-plate 1, a body section 2 and a front plate or cover 3. These parts may be separably secured together by screws 4 engaging in bosses 5 at the corners of the body section 2. lf the casing is made out of moldedmaterial, the parts 1 and 2 may be shaped as a single piece. The back-plate l of the casing is provided with a'cylindrical hub 6 by means of which the reproducer 90 is mounted on the free end of a supporting arm 7 here shown as a tube. A set-screw 8 engages in an axial slot 9 of the hub 6 to hold the reproducer in correct playing position on the arm 7, which is supposed to beproperly mounted at its other end to permit horizontal movement of the reproducer across the record,l as will be under; stood without further description.

ln casing C is mounted a magnet indicated as a whole by M. This magnet, which is preferally of the permanent steel type, is U-shaped and closely follows the rectangular outline of the casing, so as to secure a maximum length of magnet in a small space. For convenience, the magnet is here shown as secured to the back wall 1 of the casing by means of` screws 10. To 4the polar ends of magnet M are secured a pair of pole pieces P. The construction and shape of these pole pieces is best shown in Fig. 4, where it will be seen thateach pole piece comprises a pair of limbs 11 and 12. The limbs 12 are straight extensions in axial alignment and separated to provide an airgap 13. The limbs 1l project forwardly and terminate in aligned polar faces 14. Each pole piece may be formed at the rear with a downwardly extending flange 15 arranged to lie at against the body of the ma et and to receive a fastening screw 16. Additional screws 17 pass through the polar extensions 12 downwardly into the magnet. In this way, the pole pieces P are rigidly secured to the body of the magnet. In order to facilitate the assembling and adjustment of the pole pieces P, they are preferably connected by a non-magnetic plate 18, which" is fasA tened to the limbs 11 by screws 19 arranged to enter holes 20 in the pole pieces. By providing the underside of plate 18 with lugs 21 arranged to engagethe sides 22 of the pole pieces, the correct spacing of the latter is automatically accomplished by attaching the plate 18. This plate also permits the handling of the two pole pieces as a single rigid unit. i

On the polar extensions 12 is mounted a current-generating coil 23, which preferably 4fits snugly between the sides 24 of the pole pieces and is thus firmly held in place without additional fastening means. If necessary, the casing C may be formed with a bulge 24 to accommodate the coil 23. It

=is understood, of course, that'the coil 23 is inserted in position on the pole pieces before the same are connected together by the plate 18. The polar extensions 12 consti tute a magnetic core for the coil 23, and

lthe airgap 13 is of such width as to provide aV magnetic path of predetermined reluctancef As will be clear from Fig. 4, the polar extensions 11 and 12 provide parallel maonetic aths for the field flux. The' pat throug the forward projectionsll may be considered as the main ath, and the coreforming extensions 12 A orm a shunt path through the coil 23. 'i

The lower end of casing C is provided with a pair of lugs 25 carrying a suitable pivot bearing 26 for a needle arm 27, which terminates at its lower end in a needle holder 28.` A slot 29 permits the needle arm to eX- tend upwardly into the casing. The bearing 26 permits the needle arm to vibrate transversely of the casing (from left to right as viewed in Fig. 2). To the inner end of needle arm 27 is attached a magnetic vibratory strip or armature 30. The ends of this strip are secured to a pair of nonmagneticbrackets 31, as by screws 32 or otherwise. The brackets 31 are in this instance secured to the polar limbs 11 by screws 33 entering screw-holes 34 in the pole pieces. The needle arm 27 is connected tothe vibratory strip 30 at the center, so that the strip may vibrate symmetrically with respect vto the polar faces 14. The magnetic strip 30 is preferably made of resilient magnetic metal, so that it may also act as an automatic restoring and centering spring for the needle arm. Normally, the vibratory strip or armature 30 is separated from the polar faces 14 by a 'pair of airgaps 35. Since these two airgaps are in series, they may be referred to as a single airgap of normally predetermined reluctance. Preferably, the reluctance of Vthe shunt airgap 13 is made equal to the normal reluctance of the double airgap 35, so that the normal field flux divides about evenly between the shunt path 12 and the main path including the polar limbs 11 and the armatures 30. To facilitate adjustment of the relative reluctances of the airgaps 13 and 35, the nornal distance of the armature from the polar faces 14 may be regulated in any practical way. For instance, one or more shims can be interposed between the armature ends and the flanges 31' of brackets 31. Or, the fastening screws 33 may engage in longitudiynal slots in brackets 31, so as to permit adjustment of the latter along the sides of the pole pieces.

The operation of the construction above described will be clear to those skilled in the art without further explanation, but I may briefly summarize it as follows: As the needle arm vibrates under the action of the record playing needle, the armature stri 30 is moved toward and away. from the po ar faces 14. 'When the armature moves toward the pole pieces, the magnetic reluctance through the main path 11 is decreased, and therefore the greater ortion of the field flux passes outside the coi 23 through the polar extensions 11 and armature 30.. The next instant, when the armature 30 moves awa from the polar faces 14, the flux through t e shunt field 12 is increased. Consequently, this variation of flux through thecoil 23 as the armature 30 vibrates, causes current impulses to be generated in the coil, and these current impulses are an electrical representation (as it were) of the mechanical movements of the needle arm. Since the armature 30 is at a far greater distance from the pivot 26,0f the needle arm than is the point of the record needle, it is clear that the needle vibrations` are transmitted to the armature in greatly amplified ratio, so that the smallest vibrations ofthe needle produce sufficient movement of the armature to generate current impulses in coil 23. The flux lvariations in the coil are in amplified relation to the movement of the armature, because the latter simulta-v dred lines to the. inch where the needle vibrations are very delicate even Vin their maximum amplitude.

It is hardly necessary to explain that the coil 23 is supposed to be connected in a suitable circuit for operating loudspeaker mechanism. If needed, the current impulses in coil 23 may be amplified, as bymeans of radio tubes or similar devices, before operating or controlling a loudspeaker. As these circuit connections are Well understood, I need not show or describe them in detail. lt is suii'cient that I show the ends 36 of coil 23 connected to a pair of insulated binding posts 37 on the back plate 1 of the casing.

Circuit conductors 38 lead from the binding posts 3 7 to suitable amplifying apparatus or to the electromagnetic mechanism of a loudspeaker. By concealing the conductors 38 within the supporting tube 7, the neatness oit the instrument is enhanced.

The airgap 13 in the shunt path 12 need not necessarily be arranged centrally of the coil 23, for it may be provided at any other suitable point in the shunt path. For instance, in 1 `i 5 one of the pole pieces P is provided with a shunt extension 12"' which is separated from the other pole piece by an airgap 13 arranged at one end of coil 23.

When l refer to the shunt airgap 13 or 13 y as a Xed airga l do not mean that it is in all cases nonagjustable, but l use the term fixed to distinguish this airgap from the variable operative airgap 35. The airgap 13 or 13 may if desired, be adjustable to regulate the re uctance ot the shunt path in relation to the main magnetic path. For instance, one or both polar extensions 12., or the polar extension 12',` can be adjustably mounted in their respective pole pieces, as by a screw-threaded connection which allows ready adjustment oit the polar extensions in an axial direction. rllhis will be clear without the need ot additional illustration.

Although ll have shown and described my invention as an electric phonographreproducer, it is clear that the armature strip 30 may be replaced by a properly supported diaphragm adapted to be actuated by sound Waves, which are to be reproduced through the medium ot coil 23, in the manner above set forth.' When I therefore speak broadly of a vibratory magnetic member for controlling the luX of the .magnetic shunt path, l mean a member adapted to be actuated'by a needle arm, or an acousc diaphragm set in motion by sound waves, or any other magnetic member suitably set in vibration. The reproducer of my invention is equally well adapted for playing lateralcut records and vertical-cut records, depending on the way it is mounted on the supportlng arm. y

The various features of my invention may be mechanically carried out in other forms than herein set forth Without departing from the scope of the appended claims.

What I claim as my invention is:

l. An electric sound reproducer comprising a magnet having pole pieces arranged to provide a magnetic shunt path containing an airgap, said pole pieces having polar faces arranged to form an operative airgap, a coil mounted so as to be subject tothe iiunr in said shunt path, and a vibra'- tory magnetic member mounted in operative relation to said pole faces to vary said lastmentioned airgap for controlling the magnetic Hux passing through said shunt path and said coil, said member being adapted to be acoustically actuated.

2. lin an electric sound reproducer, a magnet having a pair of pole pieces, a vibratory magnetic member mounted in operative relation to the polar faces of said pole pieces, a pair ot axially aligned extensionson said pole pieces, said extensions being separated by an airgap and constituting a magnetic core of predetermined reluctance, and a coil on said core, the vibrations of said member varying the magnetic flux through said core to generate current impulses in said coil.

. 3. ln an electric phonograph reproducer, a magnet structure having pole pieces arranged to provide two parallel magnetic paths between the magnet poles, so that the field flux divides between these paths, one of said paths containing a Xed airgap and a coil, the other path including a vibratory magnetic member arranged to provide a variable airgap in said other path, so that the vibrations of said member vary the magnetic Hua through said coil, said parallel magnetic paths being so arranged that the flux passing through"v said vibratory member does not pass through 'the path containing said coil, and a needle arm connected to said member. y

4l. An electric sound reproducer comprising a magnet having pole pieces arranged to provide a magnetic shunt path containing an airgap, a coil mounted so as to be subject to the luX in said shunt path, a vibratory magnetic strip m'ounted in operative relation to said pole pieces for controlling the magnetic Hur passing through said shunt path and said coil, and a needle arm for actuating said magnetic strip.v

45. An electric phonograph reproducer comprising a magnet having a pair of pole pieces, a vibratory magnetic strip mounted 1n operative relation to the polar faces of said polel pieces, means whereby said pole pieces form a magnetic core with an airgap, said core constituting a magnetic shunt path of predetermined reluctance, a coil on s aid core, and a needle arm for vibratin said strip in amplified relation to the nee le vibrations, the vibrations of said strip varying the magnetic iux through said shunt path to' generate current impulses in said coil.

6. In an electric sound reproducer, a magnet having pole pieces constructed to provide` two parellc paths for the magnetic iiux, one of said paths having a iixed airgap and the other path having a variable airgap, `a vibratory magnetic member operatively associated with said pole pieces and included in the second-mentioned patlnfsaid airgaps beingy so proportioned that normally said paths have practically the same magnetic reluctance, and a coil arranged to be traversed by the flux in the first-mentioned path, said magnetic member being acoustically actuated to vary the reluctance of the second-mentioned magnetic path and thereby vary the 'flux through said coil.

7.4 An electric phonograph reproducer comprising a ma net structure adapted to provide two para] el magnetic paths between the magnet poles, one path containing a fixed airgap and a coil, the other path in- `cluding a vibratory magnetic member arranged to provide a variable airgap in said other path, so that vibrations of said member vary the magnetic iiux through said coil, and a needlearm connected at its inner end to said member for transmitting thereto the needle vibrations in amplified ratio.

8. In an electric sound transmitter, a magnet having pole pieces provided each with two extensions,one pair of opposite extensions terminating in aligned polar faces, the 'second pair of extensions projecting toward each other in axial. alignment andbein separated by a fixed airgap, said second pair of polar extensions forming a magnetic shunt path, a coil on said shunt extensions, and a vibratory magnetic member operatively associated with said polar faces to vary the magnetic iiux through said -shunt path and said coil.

9. In an electric phonograph reproducer, a casing adapted to be mounted on a suitable support, a magnet in said casing, said magnet having pole pieces provided each with two extensions,- one pair of opposite extensions terminating in aligned polar faces, the second pair of extensions projecting toward each other inaxial alignment and being separated by a 'fixed airgap, said second pair of polar extensions forming a magnetic shunt path, a coil on said shunt extensions, a ,vibratory magnetic member operatively associated with said polar faces to vary the magnetic flux through said shunt path and said-coil, and a needle arm connected at its inner to the center of said strip for actuating-.whe same in amplified relation to the needle vibrations, said strip acting as a centralizing and restoring spring for the needle arm.

10. In an electric sound reproducer, electromagnetic current-generating mechanism including a resilient magnetic strip supported for vibratory movement, a non-resilient vibratory member connected to said strip for actuating the same, said resilient strip also serving as a restoring spring for said member, and acoustic means for operating said member. Y

1l. In an electric sound reproducer, a magnet having a pair of pole pieces attached to the polar ends of the magnet, a non-magnetic plate for securing said pole pieces together in properly spaced relation independently of sald magnet, a pair of nonmagnetici` brackets attached to said pole pieces, a vibratory magnetic strip secured at its ends to said braclets` and arranged in operative relation to the polar faces of said pole pieces, a pair of axially aligned extensions on sai pole pieces, said extensions being separated by an airgap and comprising a magnetic core of predetermined reluctance, a coil on said core, and means for vibrating said magnetic strip.

12. In an electric sound transmitter, a magnet havingpole pieces provided each with two extensions, one pair of opposite extensions terminating in aligned polar` faces, a non-magnetic plate to which said last-named extensions are secured 1n properly spaced relation, so that said pole pieces v are rigidly connected as a unit independently of the magnet, the second air of extensions projecting toward eac other in axial alignment and being separated by an airgap, said secondpair of polar extensions forming a magnetic shunt path of redetermined reluctance, a coil on said s unt extensions, a pair of non-magnetic brackets secured to said first-mentioned 4polar extensions, a vibrator magnetic strip attached at its ends to sai brackets andfarranged in operative relation to said polar faces, and vacoustic means for vibrating said strip to vary the magnetic flux through said coil.

13. An electric sound reproducer having a magnet, a pair of separate pole"piecesu,)a

coil carried on said pole pieces, a nonmag`"- coil together as a single rigid unit, projec' tions on said member arranged to engagesaid pole pieces for spacing the same in predetermined relation, and means for securing said polar unit to the magnet.

15. In an electric sound reproducer having a magnet, a pair of separate pole pieces, a non-magnetic member for securing said pole pieces together in properly spaced relation as a single rigid unit, a vibratory armature mounted on said polar unit in operative relation to said pole pieces, a coil sup orted by and between the pole pieces of sai unit, and means independent of said member for securing said unit with its armature and coil to said magnet.

16. In an electric sound reproducer, a magnet having pole pieces constructed to provide two parallel paths between the magnet poles, one of said paths including a pair of aligned polar extensionsC with an airgap, said extensions being substantially parallel with the polar faces of said pole pieces, a coil surrounding said polar extensions, and a vibratory magnetic member mounted in operative relation to said polar faces.

17. In an electric Adevlce of the class described, a magnet having pole pieces terminating in aligned polar faces, a vibratory magnetic member in operative relation to said pole faces, means to provide a magnetic path of predetermined reluctance between said pole piecesindependently of said vibratory member, and a coil in said path, said vibratory member and said coil being so arranged that the magnetic flux passing through said member does not pass through the path containing said coil.,

18. In an electricv device of the class Y ported at its ends, a needle arm connected to the center of said resilient strip, and a coil electrically aiiected by the vibrations of said armature strip, which also acts as a centering and restoring spring for said needle arm.

20. In an electric phonograph reproducer, a magnet having pole pieces terminating in a pair ot' polar faces arranged to provide an operative airgap, a magnetic core mounted between said pole pieces to provide a shunt path with a fixed airgap, a coil on said core, a vibratory armature in operative relation to said polar faces to vary said first-mentioned airgap, said armature cooperating with said pole pieces .to form a magnetic path in parallel with said shunt path, so that vibrations of said armature decrease the magnetic ux through one path and simultaneously increase the linx through the other path, said coil and armaturebeing so arranged that the flux passing through the armature does not pass through the coil, and a needle arm for vibrating said armature.

- OLPH A. THOMAS, 

